sedimentary
Chert (Jasper/Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or yellowish-brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or via chemical precipitation in sedimentary basins. It often replaces original carbonate materials in limestone.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregate and as a semi-precious gemstone in jewelry when it exhibits unique colors.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces razor-sharp edges. It is chemically identical to quartz but has a different microscopic structure.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found as nodules in limestone or as smooth river pebbles.
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